content: /*
   * Copyright 2017 David Karnok
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package hu.akarnokd.reactive4javaflow.impl.schedulers;
  
  import hu.akarnokd.reactive4javaflow.*;
  import hu.akarnokd.reactive4javaflow.functionals.AutoDisposable;
  import hu.akarnokd.reactive4javaflow.impl.*;
  import hu.akarnokd.reactive4javaflow.impl.util.MpscLinkedArrayQueue;
  
  import java.lang.invoke.*;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicReference;
  
  public final class TrampolineSchedulerService implements SchedulerService {
      @Override
      public Worker worker() {
          return new TrampolineWorker();
      }
  
      static final class TrampolineWorker implements SchedulerService.Worker {
  
          final MpscLinkedArrayQueue<TrampolineTask> queue;
  
          long wip;
          static final VarHandle WIP = VH.find(MethodHandles.lookup(), TrampolineWorker.class, "wip", Long.TYPE);
  
          volatile boolean closed;
  
          TrampolineWorker() {
              queue = new MpscLinkedArrayQueue<>(32);
          }
  
          @Override
          public AutoDisposable schedule(Runnable task, long delay, TimeUnit unit) {
              if (!closed) {
                  TrampolineTask tt = new TrampolineTask(task, unit.toMillis(delay));
                  queue.offer(tt);
                  drain();
                  return tt;
              }
              return REJECTED;
          }
  
          @Override
          public void close() {
              closed = true;
              drain();
          }
  
          void drain() {
              if ((long)WIP.getAndAdd(this, 1) == 0) {
                  PlainQueue<TrampolineTask> q = queue;
                  do {
                      TrampolineTask tt = q.poll();
                      if (tt != null && !closed) {
                          tt.run();
                      }
                  } while ((long)WIP.getAndAdd(this, -1) - 1 != 0);
              }
          }
  
          static final class TrampolineTask extends AtomicReference<Runnable> implements Runnable, AutoDisposable {
  
              final long sleepMillis;
  
              TrampolineTask(Runnable run, long sleepMillis) {
                  this.sleepMillis = sleepMillis;
                  setRelease(run);
              }
  
              @Override
              public void close() {
                  setRelease(null);
              }
  
              @Override
              public void run() {
                  Runnable r = getAcquire();
                  if (r != null) {
                      setRelease(null);
                      try {
                          if (sleepMillis != 0L) {
                              Thread.sleep(sleepMillis);
                          }
                          r.run();
                      } catch (final Throwable ex) {
                          FolyamPlugins.onError(ex);
                      }
                  }
              }
          }
      }
  }
  